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A057708 Numbers n such that 2^n reversed is prime. 10
1, 4, 5, 7, 10, 17, 24, 37, 45, 55, 70, 77, 107, 137, 150, 271, 364, 1157, 1656, 2004, 2126, 3033, 3489, 3645, 4336, 6597, 7279, 12690, 13840, 20108, 21693, 28888, 84155, 102930 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(35) > 105000. - Giovanni Resta, Feb 22 2013

LINKS

Table of n, a(n) for n=1..34.

EXAMPLE

4 is a member because 2^4 reversed is 61 and prime.

MAPLE

with(numtheory): myarray := []: for n from 1 to 4000 do it1 := convert(2^n, base, 10): it2 := sum(10^(nops(it1)-i)*it1[i], i=1..nops(it1)): if isprime(it2) then printf(`%d, `, n) fi: od:

MATHEMATICA

Do[ If[ PrimeQ[ FromDigits[ Reverse[ IntegerDigits[2^n]] ]], Print[ n]], {n, 20000}] (* Robert G. Wilson v, Jan 29 2005 *)

Select[Range[4400], PrimeQ[IntegerReverse[2^#]]&] (* Requires Mathematica version 10 or later *) (* The program generates the first 25 terms of the sequence; to generate more, increase the Range constant, but the program will take longer to run. *) (* Harvey P. Dale, Aug 05 2020 *)

CROSSREFS

Sequence in context: A145018 A018910 A022936 * A032686 A074300 A047375

Adjacent sequences:  A057705 A057706 A057707 * A057709 A057710 A057711

KEYWORD

base,nonn,more

AUTHOR

G. L. Honaker, Jr., Oct 23 2000

EXTENSIONS

More terms from Chris Nash (chris_nash(AT)prodigy.net), Oct 25 2000

Two more terms from Robert G. Wilson v, Jan 29 2001

3 more terms from Farideh Firoozbakht, Aug 05 2004

a(33)-a(34) from Giovanni Resta, Feb 22 2013

STATUS

approved

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Last modified January 21 10:36 EST 2021. Contains 340343 sequences. (Running on oeis4.)